Introduced in 1983, the 10mm Automatic is the predecessor to the 40 S&W, which is identical in all ways excepting a shorter case and overall length; working pressure is similar. Because it can use about 5% higher pressure and has significantly greater usable case capacity, the 10mm can generate far more energy than the 40 S&W. With the best loads launching the same 180-grain bullets from 4-inch barrels, the 10mm generates almost 25% greater muzzle energy. Despite delivering significant energy and working in the same guns as the 45 Automatic, the 10mm has the advantages of being more controllable because the lighter bullets usually used generate less recoil and with modern designs it offers the shooter more rounds in the magazine when used in guns of equal size. I personally find a well-tuned Colt Delta Elite to be a wonderful pistol I can shoot well. My friend, Andy Tuttle, let me use his for a night-fighting seminar at the Whittington Center. After firing only one magazine full of ammo, I was enamored with the gun and the chambering. When loaded with the right bullet, the 10mm is probably the minimum chambering I would feel comfortable carrying in bear country as a means of last resort in case of bear attack, when I would certainly be wondering why I had not brought along a 10-gauge; or, better yet, a howitzer; or, ideally, someone I could outrun! As with any pistol round headspacing on the case mouth, best practice is to apply a taper-crimp after seating the bullet. This helps to lock the bullet in place against chambering forces that might otherwise drive it into the case. I cannot too-strongly recommend getting a second seating-and-crimping die so you can have one adjusted to only seat the bullet and the second adjusted to only taper-crimp the case mouth. Generally, attempting to do both operations in one step is a recipe for damaged and destroyed cases.